Single double backseat

ABSTRACT

A valve comprising a housing with an inlet and outlet and a chamber in between, a reciprocating gate mounted in a gate seat disposed within the chamber for opening and closing the valve, an upper bonnet for closing the chamber at one end and a lower bonnet for closing the chamber at the other end, the gate being disposed between upper and lower stems which extend into the upper and lower bonnets respectively. Metal-to-metal seals are provided at all junctures between the above members in the lower gate position with back-up seals at the junctures of all moving members. 
     A double edged seal ring integral with the upper stem self-contained within the upper bonnet provides a metal-to-metal seal with the upper bonnet in the upper and lower gate positions of the valve. 
     A metal gasket arrangement is provided between the upper bonnet and valve body whereby the assemblage of all points of contact between the gasket and body form an annular ring. 
     A combination seal ring of metal and plastic is disposed between the gate seat and valve body at the outlet whereby the metal prevents the plastic from extruding between the seat and body and into the outlet. 
     A removable backseat may be used to simultaneously seal the upper bonnet and upper stem upon moving the valve to one of its positions.

This is a continuation of application Ser. No. 655,693, filed Feb. 6,1976, now abandoned, which is a division of application Ser. No.512,368, filed Oct. 4, 1974, now abandoned.

REFERENCE TO RELATED PATENTS AND PUBLICATIONS

Two related applications also entitled High Pressure Valve are beingfiled concurrently herewith and assigned to the same assignee as thepresent application. The disclosures of the aforementioned concurrentapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to valves and especially to gate valves suitablefor high pressure service. The invention is particularly directed toimprovements in the seals and sealing arrangement for a through-conduit,rising stem high pressure gate valve.

2. Description Of The Prior Art

Gate valves have been commonly used for many years and have beenemployed in a variety of services such as in the oil and/or gas servicesof the petroleum industry. However, such valves have been designed forservice involving pressures of only several thousand pounds per squareinch. Today due to the depleted energy supply it has become necessary toexplore and produce oil and gas under very high pressures of the range30,000 psi (pounds per square inch) or more. Such high pressures haverequired greater sealing capacity and better safety features in suchvalves.

Prior art gate valves generally consist of a valve body having inlet andoutlet conduits with a chamber therebetween. A gate having an openingtherethrough is disposed in a gate seat mounted within the chamber andthe gate is mounted on a stem. The chamber is closed by a bonnet affixedto the valve housing. The stem reciprocates within the bonnet and isattached to a reciprocating apparatus for moving the gate between aclosed position in which flow is blocked through the conduits and anopen position in which flow is allowed through the conduits and the gateopening. Such a valve is illustrated in U.S. Pat. Nos. 3,538,938 and3,696,831.

A gasket seal is provided to seal between the bonnet and the valvehousing. A ring gasket has been used as shown in U.S. Pat. No.2,433,638; 2,842,336; and 3,696,831 or an o-ring seal as shown in U.S.Pat. Nos. 3,095,004 and 3,135,285. It is well known to use a standardmetal joint gasket received in grooves at the flange faces of twowellhead members as shown in U.S. Pat. Nos. 2,830,665 and 3,007,719.Such gaskets may have a diamond shaped cross-section or a T-shapedcross-section as advertised by Gray Tool Company on pages 2217-2272 inthe 1970-71 Composite Catalog published by World Oil. A resilient steelring with o-rings for sealing between a valve housing and a bonnet of agate valve is shown in U.S. Pat. No. 2,780,233.

It is well known to seal between the gate seat and the valve housing byusing an o-ring as shown in U.S. Pat. Nos. 2,957,492 and 3,348,567.Further in automatic pressure sealed gate valves shown in U.S. Pat. Nos.3,095,004; 3,538,938; and 3,696,831 fluent sealant rings are disposedaround the gate seats to provide sealing between the valve housing andgate seats in response to line pressure on fluent sealant reservoirs incommunication with the fluent sealant rings, and o-rings are installedon each side of the fluent sealant rings to isolate the fluent sealantin the fluent sealant rings from contamination by line fluids. This sameprinciple is used for seals in wellheads as shown in U.S. Pat. No.2,952,479. It is also known to locate an o-ring seal on the end of thegate seat as shown in U.S. Pat. No. 3,696,831. U.S. Pat. Nos. 3,057,630and 3,758,072 teach combining an elastomeric O-ring and apolyfluoroethylene polymer such as the brand "Teflon" or "nylon" orother low-friction plastic ring to make a seal ring. Further U.S. Pat.No. 3,103,366 teaches a deformable metal ring, as for example ofaluminum, with an inner deformable plastic ring ofpolytetrafluororoethylene whereby the metal ring can adapt itself toslightly varying recess clearances and prevent the plastic ring fromextruding through the clearances under pressure.

Generally the stem is sealed with the bonnet by means of a seal such asan o-ring, compressed sealant, or chevron packing as are shown in U.S.Pat. Nos. 2,657,989; 2,780,233; 2,842,336; 2,957,492; 3,095,004;3,181,552; and 3,696,831. Various valves such as are disclosed in U.S.Pat. Nos. 2,657,721; 2,780,233; 2,842,336; 3,348,567 show back seatswhich are actuated to provide a metal-to-metal seal between the stem andthe bonnet and/or valve housing when it is necessary to replace thepacking around the stem. U.S. Pat. No. 3,013,769 discloses two separateseat rings mounted on the stem one of which will sealingly engage thebonnet either in the open position or in the closed position of thevalve. U.S. Pat. No. 3,538,938 illustrates upper and lower stem sectionswith annular packing between the upper stem section and bonnet andbetween the lower stem section and valve housing, and further disclosesupper and lower enlargements mounted on the upper and lower stemsections respectively.

The sealing systems and arrangements of the prior art gate valves weredesigned for working pressures in the range of several thousand poundspsi and are not able to service working pressures in the range of 30,000psi. The prior art valves do not provide back-up seals if the stem sealsblow out under high pressure and the stem seals are elastomeric sealsand not metal-to-metal seals. Such sealing systems may permit theleakage of poisonous hydrogen sulfide gas under high pressure. Furthergate seat seals will extrude and roll out of the seal grooves under highpressures.

SUMMARY OF THE INVENTION

The present invention discloses a unique sealing system and arrangementfor a high pressure gate valve servicing pressures in the range of30,000 psi. In the lower gate position, dual seals are provided betweenthe upper stem and bonnet, between the lower stem and valve housing, andbetween the gate seat and valve housing. Each of such dual seals providea metal-to-metal seal with a back-up seal to prevent a blow out and toisolate the back-up seals from long exposure to line fluids.

The present system provides a unique double edged backseat disposed onthe stem and self-contained within the bonnet to sealingly engage thebonnet in either the open or closed position of the valve.

In an alternative embodiment two separate backseats, one of which is aremovable backseat, are disposed on the stem to sealingly engage thebonnet in either the open or closed position of the valve. The removablebackseat has a unique simultaneous double sealing engagement whichprovides metal-to-metal sealing engagement with both the bonnet and stemsimultaneously which prevents leakage between the removable backseat andstem and between the stem and bonnet.

The lower stem is permitted limited movement axially with respect to thegate thereby permitting a metal-to-metal seal between the lower stem andthe valve housing at the same time metal-to-metal sealing engagement ismade between the upper stem and the bonnet when the gate is in the lowerposition. The lower stem seal with the valve housing is activated byline pressure while the upper stem seal is activated mechanically.

The present application is one of three related applications in one ofwhich the entire sealing system and arrangement are claimed, in anotherthe sealing assembly is claimed, and in another the double edgedbackseat is claimed.

Other objects and advantages of the invention will appear from thefollowing description.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of a preferred embodiment of the invention,reference will now be made to the accompanying drawings wherein:

FIG. 1 is an elevation view in section of a valve according to apreferred embodiment of the invention showing the valve in the closedposition;

FIG. 2 is an enlargement of the upper and lower portions of the view ofthe valve shown in FIG. 1;

FIG. 3 is an enlargement of a portion of one of the gate seats and valvehousing shown in FIG. 1;

FIG. 4A is an axial section view of the gate seat seal shown in FIG. 3prior to installation of the gate seat in the valve housing as shown inFIG. 3;

FIG. 4B is an axial section view of the gate seat seal shown in FIG. 3after installation of the gate seat in the valve housing as shown inFIG. 3;

FIG. 5A is an axial section view of the initial mating of the bonnetgasket between the bonnet and valve housing illustrated in FIG. 1;

FIG. 5B is an axial section view of the bonnet gasket installed in thebonnet and ready for installation in the valve housing;

FIG. 6A is an axial section view of an alternative embodiment of thegate seat seal prior to installation in the valve housing;

FIG. 6B is an axial section view of the embodiment of the gate seat sealshown in FIG. 6A installed in the valve housing; and

FIG. 7 is an axial section view of an alternative embodimentillustrating a removable backseat disposed on the upper stem.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The valve, in accordance with the preferred embodiment illustrated inFIGS. 1-5, inclusive, is of the through-conduit, rising stem, gate type,comprising a valve housing or body 10 having opposed flow ports 12, 14either of which may be the inlet or outlet depending upon theorientation of the valve in the line in which the valve is mounted,forming the flowway 16 which is intersected interiorly of the housing 10by a cylindrical closure or gate chamber 18 whose axis is generally atright angles to the flow way. As illustrated, flow port 14 is theupstream portion or inlet of the valve and flow port 12 is thedownstream or outlet of the valve. The fluent material flowing throughthe line and valve shall be termed line fluids. The inner ends of flowports 14, 12 are provided with coaxial counterbores 20, 22 respectively,circumscribing flow ports 12, 14 and forming inwardly facing annularshoulders 24, 26 and inwardly facing cylindrical walls 28, 30respectively, the counterbore walls 28, 30 having a larger diameter thanthe diameter of flow ports 12, 14.

Closure chamber 18 and counterbores 20, 22 are adapted to receive a pairof gate seat members 32, 34 respectively. As gate seat members 32, 34and their appurtenances are identical in construction and are arrangedsymetrically on opposite sides of closure chamber 18, the description ofone will, it will be understood, be applicable to both.

The gate seat member 34 is elongate in form, having an inwardly facingsurface shaped to cooperate in sliding engagement with the abutting faceof gate 40, as will be described hereinafter, and an outwardly facingsurface 42 shaped to be substantially complimentary to the shape of theportion of the wall 44 forming closure chamber 18 surrounding theflowports 12, 14 and extending longitudinally of the chamber 18. In theillustrative embodiment where gate 40 is of the flat-sided form, innersurface 46 will likewise be flat. Further, gate seat member 34 includesa seat neck or hub 50 to be received by counterbore 22. Gate seat member34 is provided with a transverse opening 52 coaxial and registering withflow port 12 and flowway 16 and generally of the same diameter toprovide full open flow therethrough.

The upper end portion of gate seat member 34 is bored from its outer endto provide a reservoir 54, adapted for receiving a flowable or fluentsealant 56, such as is conventionally used in automatically sealingvalves. A cylindrical piston or barrier 57 is slidably mounted inreservoir 54 for pressurizing the sealant as will be subsequentlydescribed. Referring now to FIG. 3 the lower end of reservoir 54communicates through a longitudinal passage 58 with a passage 60 whichextends transversely through the body of the gate seat member 34 to theouter peripheral surface 62 of seat hub 50. The outer end of transversepassage 60 communicates with an annular sealant groove 64 formed inouter surface 62 of gate seat member 34 encircling opening 52. The lowerend of reservoir 54 also communicates through a transverse passage 66which communicates with the exterior of inner face 46 of gate seatmember 34 and is spaced from an annular sealing groove 68 formed ininner surface 46 encircling opening 52.

Referring to FIG. 3 a threaded socket 234, shown generally, is formed inthe side of body 10 and is adapted to receive a conventional pressurefitting for introducing sealant material 56 into socket 234. With thisarrangement, it will be seen that sealant 56 introduced through thefitting will be forced via passage 236 through groove 64, thence viapassage 60 and 58 into the interior of reservoir 54 below barrier 57.

Referring again to FIG. 1, there is further included a closure means 40'having a gate 40 disposed in closure chamber 18 for verticalreciprocation across the flowway 16 between the gate seats 32, 34. Thegate 40 is constructed of a pair of mating generally rectangular gatesegments, 70, 72 having flat outer faces adapted for slidable engagementwith the inner end faces 45, 46 of the seat members 32, 34. The gate 40is provided near its lower end with a transverse flow port 74, definedby registered openings in gate segments 70, 72, and adapted to registerwith openings 52, 53 in seat members 32, 34 when the gate 40 is in theraised or flowway-opening position. The upper portions of the gatesegments 70, 72 form the closure section 76 which is adapted to cut offflow through flowway 16 when the gate is in the lower or flowway-closingposition as seen in FIGS. 1, 2, and 3. The upper portion of gate segment72 is provided on its outer face with a jumper recess 78 shown in FIG. 3adapted to communicate sealant groove 68 with the inner end oftransverse passage 66 when gate 40 and gate segment 72 are in theflowway-closing position as shown in FIG. 3. It will be understood thatwhen the gate 40 is moved upwardly to the flowway-opening position, thecorresponding displacement of recess 78 will serve to disconnect groove68 from passage 66.

It should be understood that the valve shown in the figures is normalacting in that during service of the valve it is anticipated that thevalve will generally be closed to fluid flow. However the valve couldobviously be reverse acting whereby during service the valve wouldgenerally be in the open position. The normal acting valve shown can bemade reverse acting by merely modifying gate segments 70, 72 wherebytransverse flow port 74 will register with openings 52, 53 when the gateis in the lower position rather than in the upper position as previouslydescribed. Note that regardless of whether the valve is normal acting orreverse acting, the normal position (i.e. the general position of thevalve during operation) will occur when the gate 40 is in the lowerposition.

Referring now to FIGS. 3, 4A and 4B, seals 230, 240 are received inannular grooves 232, 242 which circumscribe seat hub 50 for sealing withsurface 30 of housing 10 on opposite sides of the sealant groove 64.Seal 230 is in elastomeric or plastic o-ring seal while seal 240 is anintegral plastic-metal seal ring. Seal 240 includes an annular metalring 244 and a polyfuoroethylene polymer such as the brand "Teflon","nylon", or other low-friction plastic annular ring 246. Groove 242 islocated at the outer peripheral corner of hub 50 whereby groove 242 istwo-sided with the opposing surfaces of counterbore 22 providing theother two sides. Ideally the thickness of seal 240 will be equal to thelength of the groove 242 with the tolerance being on the side of seal240 having a greater thickness. Preferably the volume of groove 242 willsubstantially equal the volume of seal 240. The metal ring 244 has aclose fit around groove 242 and is preferably press fitted onto groove242. Upon assembly as shown in FIGS. 1 and 4B gate seat members 32, 34are inserted into closure member 18 whereby opposing seat hubs 50, 51are inserted into corresponding counterbores 20, 22 respectively. Theleading edges 21, 23 at the entrances of counterbores 20, 22respectively are beveled to facilitate the assembly of hubs 50, 51. Uponassembly the metal ring 244 engages the bottom of groove 242 andshoulder 26 of counterbore 22 with plastic ring 246 substantiallyfilling the remainder of groove 242.

The surfaces between shoulder 26 of counterbore 22 and the end face 243of hub 50 cannot be matingly machined to effect a proper seal therebyrequiring seal 240. However, such machining may be accomplished for aproper metal-to-metal sealing engagement between the outer wall 73 ofgate segment 72 and the inner surface 46 of gate seat member 34. Furtherit should be noted that to effect an adequate seal with seal 240, thearea of the radially extending annular wall 243 of groove 242 facingtowards shoulder 26 of counterbore 22 must be less than the area of gatesegment 72 encircled by sealant groove 68 exposed to line pressurethrough port 12. If the pressure on wall 243 due to sealant 56 isgreater than the pressure on gate segment 72 due to line pressure, wall243 will tend to move away from shoulder 26 thereby disengaging seal240.

Referring now to FIGS. 1 and 2, gate 40 is reciprocated by means of apressure balanced stem having an upper stem member 80 and a lower stemmember 82. Closure means 40' includes the pressure balanced stem. Lowerstem member 82 includes a head 84 at its upper end which is enclosedbetween gate segments 70, 72 within counterbores 86, 88 in the innerfaces of the lower portions of segments 70, 72. Counterbores 86, 88 havesufficient axial length to permit limited axial movement of head 84 withrespect to gate 40. Upper stem member 80 includes a T-shaped lug member90 threaded or welded onto the lower end of upper stem member 80. TheT-shaped lug member 90 is also enclosed between gate segments 70, 72within corresponding T-shaped and semi-circular counterbores 92, 94.This structure is old and forms no part of the present invention,therefore a more detailed description has not been made.

The lower end of the valve housing 10 is provided with a bore 95 coaxialwith chamber 18 and with a counterbore 96 opening from the outer end ofhousing 10 forming a stuffing box for receiving lower stem member 82 andadapted to receive an annular packing 98 under compression by acompression ring 100 and a gland 102 protruding from a lower closure cap104 secured to the housing 10 by cap screws 106 or possibly by bolts.The housing 10 and closure cap 104 have corresponding mating annulargrooves 108, 110 for receiving a lower ring gasket 112 to provide ametal-to-metal seal therebetween. The lower closure cap 104 has a bore114 for slidingly receiving the lower stem member 82. A transversepassage 116 in closure cap 104 provides communication between bore 114and bleeder valve 118 to relieve any build up of line fluids in bore114. The lower stem member 82 reciprocates in response to reciprocalmovement of the gate 40, and packing 98 serves to slidably seal aboutthe lower stem member 82.

There is provided on the upper portion of lower stem member 82 belowhead 84 a metal seat ring 120 defining a downwardly facing annularshoulder 122 surrounding the lower end of seat ring 120. Shoulder 122 isarcuate and cooperates with a bevelled seat 124 located at the entranceof bore 95 at the bottom of chamber 18 forming a line contact and ametal-to-metal seal therewith as will be described subsequently.

Referring to FIG. 2 the upper end 128 of chamber 18 is adapted to beclosed by means of a tubular cap or bonnet 130 having a closure flange132 secured to the upper end 134 of housing 10 by means of studs 136 orpossibly by bolts or capscrews. Bonnet 130 has an axial bore 138 forreceiving upper stem member 80. Upper stem member 80 has a double sealor backseat 220 radially projecting from and integral (i.e. the backseat220 and stem 80 are one piece) with upper stem 80 thereby preventing anyleakage behind the backseat 220. Backseat 220 has upwardly facing anddownwardly facing rounded shoulders 222, 224 and stress relief grooves226, 228 adjacent thereto on each side of backseat 220. Shoulders 222,224 are placed approximately back to back to limit the longitudinaldimension of bonnet 130.

Axial bore 138 includes an enlarged portion 154 having a diametergreater than the diameter of backseat 220 for receiving same. Enlargedportion 154 terminates in a lower counterbore 158 which is adapted toreceive closure ring 160 having an axial stem-receiving bore 184 coaxialwith closure chamber 18 and bonnet bore 138. In the assembly of thevalve upper stem member 80 is inserted into bore 138 with enlargedportion 154 receiving backseat 220. Closure ring 160 then slides aroundupper stem member 80 behind backseat 220 and is received by counterbore158. It is at this time that lug member 90 is threaded onto upper stemmember 80 for attachment with gate 40 and gate 40 is inserted betweengate seat members 32, 34.

Closure ring 160 when received within counterbore 158 makes enlargedportion 154 into a chamber for the reciprocation of backseat 220.Enlarged portion 154 forms an internal downwardly facing beveledshoulder or seat 156 and ring 160 includes an upwardly facing beveledconical shoulder or seat 186 at the upper end of bore 184 opposingshoulder 156 after assembly.

Backseat 220 and seat ring 120 are formed in spaced apart relation onupper stem 80 and on lower stem 82 respectively whereby in the closedflowway position, backseat 220 will sealingly engage shoulder 186providing a metal-to-metal seal therebetween and seat ring 120 willsealingly engage shoulder 124 providing a seal therebetween as the linefluid pressure forces seat ring 120 downwardly by means of the limitedaxial movement of head 84 within counterbores 86, 88. Backseat 220 isalso spaced on upper stem 80 whereby in the open flowway position seat220 will sealingly engage shoulder 156 providing a metal-to-metal sealtherebetween.

The closure ring 160 and its appurtenances are identical in constructionand are arranged symmetrically on both upper and lower sides to permitreversability, so the description of one will be applicable to both.Ring 160 includes an upper and lower ring gasket groove 162, 164 forreceiving upper and lower metal ring gaskets 166, 168 for sealingbetween the bonnet 130 and ring 160 and ring 160 are housing 10. Ringgasket groove 164 includes a downwardly and inwardly facingfrusto-conical seat or shoulder 188, a downwardly facing inner annularshoulder 190, a downwardly and outwardly facing beveled conical shoulder192, and a downwardly facing outer annular shoulder 194. Shoulders 188,190, 192 and 194 having decreasing diameters respectively. The bottomportion of counterbore 158 includes a ring gasket groove 196 having thesame features and dimensions as groove 164. Further ring gasket grooves108, 110 in lower housing 10 and cap 104 have the same features,dimensions and arrangements as grooves 196, 162. At the mouth of closurechamber 18 there is an inwardly extending annular boss 198 bounded byupper and lower frusto-conical shoulders or seats 200, 202. Shoulder 200mates and opposes shoulder 188 on closure ring 160. However, there is nocorresponding upwardly facing annular shoulder on boss 198 opposingshoulder 194 on closure ring 160.

Ring gaskets 112, 166 and 168 are identical in dimension forinterchangeability and therefore a description of one will apply to all.

Referring now to FIGS. 5A and 5B, ring gasket 168 is an annular ringhaving a T-shaped cross section. The stem 169 of the T-shaped crosssection lies in a horizontal plane perpendicular to the axis of the bore173 of the gasket 168 and the head 171 of the T-shaped cross sectionlies in a vertical plane parallel to the axis of the bore 173. The outerperipheral annular edges 204, 206 of the head 171 are beveled forengagement with annular seats or shoulders 188, 200 respectively. Gasket168 is made of metal, preferably steel.

FIG. 5A illustrates the initial assembly position of gasket 168, beforethe gasket is compressed. The dimension X between closure ring 160 andhousing 10 is approximately twice the dimension Y between stem 169 andshoulder 194 whereby as studs 136 are tightened, bonnet 130 and closurering 160 will move downwardly the distance Y until annular shoulder 194contacts the upwardly facing surface of stem 169 of gasket 168. Thisposition is illustrated in FIG. 5B at which time the dimension Z betweenclosure ring 160 and housing 10 is approximately one-half the dimensionX. Upon tightening studs 136, gasket 168 is engaged at points 208, 210by closure ring 160 and is forced against shoulder 200 until theconnection is complete as shown in FIG. 1 and 2. As shown in FIG. 2,gasket 168 has surface-to-surface contact at 211 with shoulder 200 ofhousing 10. Upon completion of the assembly gasket 168 engages closurering 160 at points, the assemblage or loci of which, forms two annularrings, and gasket 168 engages housing 10 at points, the assemblage orlocus of which, forms a single annular ring. During the assembly bevelededges 204, 206 are deformed against shoulders 188, 200 therebyestablishing a high pressure metal-to-metal seal. Such deformationoccurs because the median diameters of corners 204, 206 are slightlylarger than the median diameters of shoulders 188, 200.

Standard metal ring gasket seals, as illustrated in FIGS. 5A and 5B at212, which is slightly different than that shown in FIG. 1, may be usedin grooves 162, 196, and 108, 110 since the ring grooves are symmetricalwith opposing surfaces. However, such gaskets cannot be used betweenbonnet 130 and housing 10 because there is no upwardly facing annularshoulder on boss 198 corresponding to shoulder 194 on ring 160 aspreviously shown. The lack of this shoulder causes a standard gasketring to be unstable, to rock under load and to misalign on shoulder 200during assembly thereby providing a bad seal. If gasket 168 attempts tocock, stem 169 engages shoulder 208 which forces gasket 168 back intoalignment. To place a shoulder on boss 198 would require a largerhousing 10 and a larger bonnet 130 to provide clearance for theinstallation and removal of gate 40 and gate seat members 32, 34.

Referring now to FIG. 1, upper stem member 80 is provided with anexternally threaded portion 170 at its upper end which extends throughstuffing box 142 wherein packing 144 serves to slidably seal about thestem member 80. An internally threaded drive nut 172 extends into cap152 and is internally threaded at 174 to threadingly engage threadedportion 170 whereby rotation of the nut 172 will serve to raise andlower the closure member, i.e. stem members 80, 82 and gate 40, inaccordance with the direction of the rotation of the nut 172, in orderto move the gate 40 between flowway-opening and flowway-closingpositions. The lower end of the nut 172 has an annular flange 173 whichsupports upper antifricition bearings 176 against the top of cap 152 andbears against lower antifriction bearings 178 which rest on gland 150.The upper portion of the nut 172 which projects above the cap 152, isprovided with conventional flats at 180 for mounting an operating wheel182 or other conventional operator, by which the gate 40 is actuated.

A bleeder valve 223 communicating with bore 138 by means of passage 225through bonnet 130 provides a means to relieve bore 138 of any build upof line fluids when packing 144 is to be replaced.

The metal-to-metal seals at 156, 222; 186, 224; and 120, 124 isolatepacking 144 and 98 from long exposure to line fluids thereby preservingpacking 98, 144 from deterioration. Further the packing 98, 144 and suchmetal-to-metal seals provide dual sealing as a safety feature so if oneseal blows or ruptures, there is a back up seal. Such metal-to-metalseals also provide the capability to remove and replace packings 98, 144while the valve is under pressure although packings 98 and 144 aredesigned to operate throughout the life of the valve.

In operation as the valve is closed by operator 182, upper stem 80, gate40, and lower stem 82 more downwardly into the lower position. Seat 120on lower stem 82 seals with shoulder 124. Seat 120 is not mechanicallyactuated into sealing engagement but the line pressure forces seat 120into sealing engagement with shoulder 124. Such movement by seat 120 isallowed by the limited axial movement permitted between head 84 and gate40. Backseat 220 then engages shoulder 186 forming a metal-to-metalseal. After seat 120 engages shoulder 124, further movement downwardlyby upper stem 80 drives backseat 220 onto shoulder 186. As the valve isopened by operator 182, backseat 220 travels upwardly until backseat 220sealingly engages shoulder 156 providing a metal-to-metal seal.

In closing or opening the valve, bleeder valve 118 should be openwhereby the line pressure will provide a balanced pressure force on boththe lower stem 82 and upper stem 80. Without such a balanced pressurizedstem, the pressure on the upper stem 80 would place such a load on stem80 as to require a very high torque to be used on stem 80 to open andclose the valve. Bleeder valve 118 is used to bleed out pressure belowlower stem 82 so as to prevent any upward pressure on stem 82.

It will be seen that when the gate 40 is moved to the flowway-closingposition, shown in FIG. 1, the differential line pressure across theclosed valve will act on the downstream reservoir 54, the differentialline pressure being exerted against the barrier 57 urging it inwardly ofreservoir 54 and simultaneously forcing sealant 56 from reservoir 54into sealant groove 64 to seal off between outer surface 62 of the hub50 and the surrounding wall 30 of chamber 18, and through passage 66 andrecess 78 into sealant groove 68 provided at the inner surface of theseat member 72 to seal about the opening between the seat member 34 andthe related closure segment 72. Thus, sealant seals will automaticallybe provided between both surfaces 46, 62 of the seat member 34 and therelated portions of the closure segment 72 and the wall 30 of chamber18. The sealing action will be simultaneous.

Seals 230, 240 will be effective to prevent loss of sealant 56 fromsealant groove 64. This permits effective sealing of the exterior ofseat hub 50 while assuring against loss of sealant 56 due to any gapbetween the hub 50 and body 10 at counterbore 22.

As line pressure reaches 30,000 psi, the yield strength of ordinarysealing materials is approached under confined stress. Even below yieldstress, there is substantial movement so that ordinary o-rings will nothold. The differential pressure between chamber 18 and sealant groove 64is very low but the differential pressure between groove 64 and port 14is very high placing much pressure on seal 240. However, as highpressure is placed on plastic ring 246, metal ring 244 is forced intothe corner of groove 242 closing any gap or clearance at the downstreamjuncture of the hub 50 and housing 10 and preventing the plastic ring246 from extruding through any downstream clearance between the end face243 of hub 50 and shoulder 26. The metal ring 244 can adapt itself tovarying clearances between the hub 50 and housing 10 so that there arenot critical. Thus the high pressure helps the seal.

FIGS. 6A and 6B illustrate an alternative sealing system for sealantgroove 64 by sealing between surface 62 of hub 50 and wall 30 ofcounterbore 22. As shown in the unassembled position in FIG. 6A, aplastic seal ring 300 is received in annular groove 302 in hub 50interiorly of sealant groove 64. On the outer end portion of hub 50 is areduced diameter portion 304 having an annular channel 306 on the outerend of portion 304. A plastic seal ring 308 is slipped over the portion304 against annular shoulder 310 formed by the reduction in diameter ofportion 304. Two annular wedge or cam rings 312, 314 having opposingupwardly and downwardly facing bevels are slipped over portion 304. Thena split backup ring 316 having two semi-circular sections and aninwardly extending annular projection 318 is installed by insertingannular projection 318 into channel 306. Projection 318 has a shorterlength than the depth of channel 306. For assembly purposes the outerperipheral corner of backup ring 316 is chamfered for ease of insertionof hub 50 by contacting bevel 23 of housing 10. Further bevel 23 forcesplastic rings 300, 308 into compression within grooves 302 and portion304.

Upon expansion of the annular channel formed between reduced portion 304and wall 30 due to line pressure, as shown in FIG. 6B, wedge ring 312will tend to cam onto wedge ring 314 creating a metal-to-metal sealingengagement between portion 304 and wall 30. Further such sealingengagement will prevent the extrusion of plastic seal ring 308 as shownin FIG. 6B. Such camming or wedging of rings 312, 314 occurs from theradial support from housing 10 and hub 50.

An alternative embodiment to the integral double backseat 220 isillustrated in FIG. 7. The upper stem member 400 includes a removablebackseat seal 402 and an integral single backseat seal 404. In thisembodiment closure ring 160 may or may not be used. Ring 160 is nolonger necessary because without integral double backseat 220 on upperstem member 80, upper stem member 80 could be received into bore 406.

Bonnet 408 includes an inwardly radially extending boss 410 having anupwardly facing beveled shoulder 412 for engagement with backseat 402and a downwardly facing beveled shoulder 414 for engagement withbackseat 404.

Backseat 404 is disposed on upper stem member 400 above lug member 416and in spaced relation with the opening of the gate whereby in theraised or open flowway position backseat 404 sealingly engages shoulder414 creating a metal-to-metal seal.

The upper portion 418 of upper stem member 400 has a reduced diametercreating upwardly facing annular shoulder 420. Removable backseat 402 isslipped over reduced portion 418 being of such a diameter as to engageshoulder 420. Spaced above the backseat 402, a distance equal to thethickness of backseat 402, is disposed an annular groove 422 forreceiving split ring 424. A snap ring 426 is received in annular groove428 in the outer periphery of split ring 424 to hold split ring 424 inposition in groove 422.

Bonnet 408 includes a counterbore 430 coaxial with and adjacent to bore406. Counterbore 430 is a stuffing box receiving a lower compressionring 432 resting on the upwardly facing annular shoulder 434 created bycounterbore 430, a packing 436, and a follower compression ring 438 foractuation by gland 440 as gland 440 is threadingly received withincounterbore 430.

A bleeder valve 442 is provided for communication with bore 406 by meansof passage 444 to bleed pressure in order to change packing 436.

Backseat 402 has a downwardly extending annular seal flange 446 whichhas a lip 448 curving radially inwardly toward the stem 400. Backseat402 is made of metal as for example steel. Backseat 402 is disposed onupper stem member 400 in such spaced relation that upon movement of thegate (not shown) to the closed flowway position, backseat 402 sealinglyengages shoulder 412 by means of seal flange 446 and the engagement offlange 446 on shoulder 412 cams lip 448 into sealingly engagement withupper stem 400 to effect a metal-to-metal seal. Thus backseat 402simultaneously seals at two points, shoulder 412 and stem 400.

Backseat 404 is disposed on upper stem member 400 above lug member 416and in spaced relation with the opening of the gate whereby in theraised or open flowway position backseat 404 sealingly engages shoulder414 creating a metal-to-metal seal.

The above are, of course, merely exemplary of possible changes orvariations.

Because many varying and different embodiments may be made within thescope of the inventive concept herein taught, and because manymodifications may be made in the embodiments herein detailed inaccordance with the descriptive requirements of the law, it is to beunderstood that the details herein are to be interpreted as illustrativeand not in a limiting sense.

What is claimed as invention is:
 1. A valve comprising:a valve bodyhaving an inlet and an outlet with a chamber therebetween; closure meansfor preventing flow through said chamber into said outlet in the closedposition and permitting flow through said chamber into said outlet inthe open position; moving means for moving said closure means betweenthe open and closed positions; first and second cap members sealinglymounted on said body and having means for providing sealing closures forsaid chamber, said closure means disposed in said chamber and extendingthrough opposite sides of said chamber and into said first and secondcap members; ring means on said closure means for providing ametal-to-metal sealing engagement with said first cap member in at leastone of the open and closed positions; and single seal ring means on saidclosure means for providing a metal-to-metal sealing engagement withsaid valve body in said one of the open and closed positions, saidclosure means including means for permitting limited longitudinal axialreciprocation of said single seal ring means with respect to said ringmeans.
 2. A valve according to claim 1 wherein said ring means includesa double edged metal seal ring integral with a portion of said closuremeans which extends into said first cap member.
 3. A valve according toclaim 2 wherein said double edged metal seal ring has a substantiallysemi-circular cross section.
 4. A valve comprising:a valve body havingan inlet and an outlet with a chamber therebetween; closure means forpreventing flow through said chamber into said outlet in the closedposition and permitting flow through said chamber into said outlet inthe open position; moving means for moving said closure means betweenthe open and closed positions; first and second cap members sealinglymounted on said body and having means for providing sealing closures forsaid chamber, said closure means disposed in said chamber and extendingthrough opposite sides of said chamber and into said first and secondcap members; ring means on said closure means for providing ametal-to-metal sealing engagement with said first cap member in at leastone of the open and closed positions; single seal ring means on saidclosure means for providing a metal-to-metal sealing engagement withsaid valve body in said one of the open and closed positions; said ringmeans including a double edged metal seal ring integral with a portionof said closure means which extends into said first cap member; saidclosure means including two stress relief grooves; and said double edgedmetal seal ring being disposed on said closure means between said twostress relief grooves.
 5. A valve comprising:a valve body having aninlet and an outlet with a chamber therebetween; closure means forpreventing flow through said chamber into said outlet in the closedposition and permitting flow through said chamber into said outlet inthe open position; moving means for moving said closure means betweenthe open and closed positions; first and second cap members sealinglymounted on said body and having means for providing sealing closures forsaid chamber, said closure means disposed in said chamber and extendingthrough opposite side of said chamber and into said first and second capmembers; ring means on said closure means for providing a metal-to-metalsealing engagement with said first cap member in at least one of theopen and closed positions; single seal ring means on said closure meansfor providing a metal-to-metal sealing engagement with said valve bodyin said one of the open and closed positions; said ring means includinga double edged metal seal ring integral with a portion of said closuremeans which extends into said first cap member; and said first capmember including a bore having a first and a second metal seat; saiddouble edged metal seal ring sealingly engaging said first metal seat inthe open position and said second metal seat in the closed position. 6.A valve according to claim 1 wherein said ring means is actuated by saidmoving means.
 7. A valve comprising:a valve body having an inlet and anoutlet with a chamber therebetween; closure means for preventing flowthrough said chamber into said outlet in the closed position andpermitting flow through said chamber into said outlet in the openposition; moving means for moving said closure means between the openand closed positions; first and second cap members sealingly mounted onsaid body and having means for providing sealing closures for saidchamber, said closure means disposed in said chamber and extendingthrough opposite sides of said chamber and into said first and secondcap members; ring means on said closure means for providing ametal-to-metal sealing engagement with said first cap member in at leastone of the open and closed positions; single seal ring means on saidclosure means for providing a metal-to-metal sealing engagement withsaid valve body in said one of the open and closed positions; andsecondary seals providing back up sealing for said ring means betweensaid closure means and said first cap member.
 8. A valve according toclaim 1 further comprising means for bleeding line fluid from said firstcap member.
 9. A sealing system for valve members of a high pressurevalve including a valve body having upstream and downstream conduits, abonnet mounted on the body, an upper stem and a lower stem mountedwithin the valve body and bonnet and having a gate disposedtherebetween, a gate seat disposed within the body in sliding engagementwith the gate, and the valve having a normal position for the gate, theimprovement comprising:metal-to-metal seals in the normal positionbetween the bonnet and upper stem and the lower stem and body, saidseals being actuated at least in part by movement of said upper stem andlower stem, respectively.
 10. A sealing system according to claim 9further including back-up seals between the bonnet and upper stem andthe lower stem and body.
 11. A valve comprising:a valve body having aninlet and an outlet with a chamber therebetween; closure means forpreventing flow through said chamber into said outlet in the closedposition and permitting flow through said chamber into said outlet inthe open position; means for moving said closure means between the openand closed positions; first and second cap members sealingly mounted onsaid body and having means for providing metal-to-metal sealing closuresfor said chamber; said closure means disposed in said chamber andextending through opposite sides of said chamber and into said first andsecond cap members; double seal ring means on said closure meansproviding a metal-to-metal sealing engagement with said first cap memberin both the open and closed positions; and single seal ring means onsaid closure means providing a metal-to-metal sealing engagement withsaid valve body in one of the open and closed positions.
 12. A valveaccording to claim 11 wherein said double seal ring means includes adouble edged metal seal ring integral with a portion of said closuremeans which extends into said first cap member.
 13. A valve according toclaim 12 wherein said double edged metal seal ring has a substantiallysemi-circular cross section.
 14. A valve according to claim 12 whereinsaid double edged metal seal ring is disposed on said closure meansbetween two stress relief grooves.
 15. A valve according to claim 12wherein said first cap member includes a bore having a first and secondmetal seat; said double edged metal seal ring sealingly engaging saidfirst metal seat in the open position and said second metal seat in theclosed position.
 16. A valve according to claim 15 wherein said singleseal means includes a second metal seal ring integral with anotherportion of said closure means which extends into said second cap member;said valve body having a second metal seat at the passage of said otherportion of said closure means from said chamber; and said second metalseal ring sealingly engaging said second metal seat in one of the openand closed positions.
 17. A valve according to claim 11 wherein in thenormal position said double seal ring means shall initiate sealingengagement with said first cap member after the sealing engagement bysaid single seal ring with said valve body.
 18. A valve according toclaim 11 wherein said double seal ring means is actuated by said movingmeans and said single seal ring means is actuated by line pressure. 19.A valve according to claim 11 further comprising secondary sealsproviding back up sealing for said double seal ring means and saidsingle seal ring means between said closure means and said first capmember and said valve body.
 20. A valve according to claim 11 furthercomprising means for bleeding line fluid from said first and second capmembers.
 21. The valve of claim 11 wherein said second cap memberencloses said single seal ring means and includes seal means to providea metal-to-metal sealing engagement with said valve body when saidsingle seal ring means is in the other of the open and closed positions.22. The valve of claim 21 wherein said seal means includes a bleedervalve and metal-to-metal seals with said valve body.
 23. A high pressurevalve including a valve body having inlet and outlet conduits and anupper aperture with a chamber therebetween and a bonnet covering theupper aperture, an upper stem and a lower stem mounted within the valvebody and having a gate disposed therebetween, a gate seat disposedwithin the chamber in sliding engagement with the gate, an open positionwhere the gate permits flow through the conduits and a closed positionwhere the gate blocks flow through the conduits, and moving means formoving the gate between the open and closed positions, the improvementcomprising:first seal means disposed on the upper stem for sealingengagement with the valve body bonnet upon movement of the gate into oneof the positions by the moving means; and second seal means disposed onthe lower stem for sealing engagement with the valve body upon linepressure activation, said second seal means including means forpermitting said second seal means to be actuated prior to the sealingengagement of said first seal means.
 24. A valve, comprising:a valvebody having an upper and lower portion and an inlet and an outlet with achamber therebetween; closure means for preventing flow through saidchamber into said outlet in the closed position and permitting flowthrough said chamber into said outlet in the open position, said closuremeans disposed in said chamber and extending through opposite sides ofsaid chamber; moving means for moving said closure means between theopen and closed positions; and seal ring means on said closure means forproviding a metal-to-metal sealing engagement with said upper and lowerportions in one of said open or closed positions, said upper and lowerportions each having a seat, said seal ring means including a firstmetal seal ring disposed on said closure means and having means forsealingly engaging the seat of one of said upper and lower portions anda second metal seal ring disposed on said closure means and having meansfor sealingly engaging the seat of the other of said upper and lowerportions, said closure means having means for permitting limited axialtravel of said second metal seal ring with respect to said first metalseal ring.
 25. A valve, comprising:a valve body having an upper andlower portion and an inlet and an outlet with a chamber therebetween;closure means for preventing flow through said chamber into said outletin the closed position and permitting flow through said chamber intosaid outlet in the open position, said closure means disposed in saidchamber and extending through opposite sides of said chamber; movingmeans for moving said closure means between the open and closedpositions; seal ring means on said closure means for providing ametal-to-metal sealing engagement with said upper and lower portions inone of said open or closed positions; said seal ring means including afirst metal seal ring integral with said closure means having firstmeans for sealingly engaging said upper portion and a second metal sealring having second means for sealingly engaging said lower portion andbeing mounted on said closure means, said upper portion having a firstmetal seat for sealingly engaging said first means; said lower portionhaving a second metal seat for sealingly engaging said second means;said closure means including third means and said second metal seal ringincluding fourth means for reciprocatably holding said second metal sealring on said closure means.
 26. A valve, comprising:a valve body havingan upper and lower portion and an inlet and an outlet with a chambertherebetween; closure means for preventing flow through said chamberinto said outlet in the closed position and permitting flow through saidchamber into said outlet in the open position, said closure meansdisposed in said chamber and extending through opposite sides of saidchamber; moving means for moving said closure means between the open andclosed positions; seal ring means on said closure means for providing ametal-to-metal sealing engagement with said upper and lower portions inone of said open or closed positions; said seal ring means includes afirst metal seal ring integral with said closure means having firstmeans for sealingly engaging said upper portion and a second metal sealring having second means for sealingly engaging said lower portion andbeing mounted on said closure means, said upper portion having a firstmetal seat for sealingly engaging said first means; said lower portionhaving a second metal seat for sealingly engaging said second means;said second metal seal ring including means for initiating sealingengagement by said second means with said second metal seat in said oneof said open or closed positions prior to said first means initiatingsealing engagement with said first metal seat.
 27. A valve, comprising:avalve body having an upper and lower portion and an inlet and an outletwith a chamber therebetween; closure means for preventing flow throughsaid chamber into said outlet in the closed position and permitting flowthrough said chamber into said outlet in the open position, said closuremeans disposed in said chamber and extending through opposite sides ofsaid chamber; moving means for moving said closure means between theopen and closed positions; seal ring means on said closure means forproviding a metal-to-metal sealing engagement with said upper and lowerportions in one of said open or closed positions; said seal ring meansincluding a first metal seal ring integral with said closure meanshaving a first means for sealingly engaging said upper portion and asecond metal seal ring having second means for sealingly engaging saidlower portion and being mounted on said closure means, said upperportion having a first metal seat for sealingly engaging said firstmeans; said lower portion having a second metal seat for sealinglyengaging said second means; said second seal ring including initiationmeans for initiating sealing engagement of said second means with saidsecond metal seat upon actuation of said initiation means by linepressure and said first metal seal ring is actuated by said movingmeans.
 28. A valve comprising:a valve body having an upper and lowerportion and an inlet and an outlet with a chamber therebetween; closuremeans for preventing flow through said chamber into said outlet in theclosed position and permitting flow through said chamber into saidoutlet in the open position, said closure means being disposed in saidchamber and including a closure member and lower stems on said closuremember extending through opposite sides of said chamber; moving meansfor moving said closure means between the open and closed positions;seal ring means on said lower stem of said closure means for providing ametal-to-metal sealing engagement with said lower portion in one of saidopen or closed positions; said seal ring means including a metal sealring for sealingly engaging said lower portion; and said metal seal ringincluding means responsive to line pressure for actuating said sealingengagement of said metal seal ring and said lower portion, said meansresponsive to line pressure including means for permitting limitedlongitudinal axial travel of said lower stem with respect to saidclosure member.
 29. In a valve comprising a body having inlet and outletconduits and upper and lower stem apertures with a chamber therebetween,a closure disposed in said chamber and movable between an open positionwherein fluid flow is permitted through said chamber and into saidoutlet conduit and a closed position wherein such flow is prevented,upper and lower stems on said closure member extending through saidupper and lower apertures, respectively, an upper bonnet covering theupper aperture, a lower cap covering the lower aperture, and meansconnected to one of said stems adapted to move said stems longitudinallyand thereby move said closure member between open and closed positions,the improvement which comprises:closing means on said stems movable,upon movement of said closure member to one of said open and closedpositions, to a position closing both of said upper and lower apertures;said closing means on said stems including a metal seal member on eachof the upper and lower stems; and a metal seat surrounding each of theupper and lower apertures, each engageable by one of said seal members,such lower stem being longitudinally reciprocatably mounted on suchclosure member.
 30. In a valve comprising a body having inlet and outletconduits and upper and lower stem apertures with a chamber therebetween,a closure member disposed in said chamber and movable between an openposition wherein fluid flow is permitted through said chamber and intosaid outlet conduit and a closed position wherein such flow isprevented, upper and lower stems on said closure member extendingthrough said upper and lower apertures, respectively, an upper bonnetcovering the upper aperture, a lower cap covering the lower aperture,and means connected to one of said stems adapted to move said stemslongitudinally and thereby move said closure member between open andclosed positions, the improvement which comprises:closing means on saidstems movable, upon movement of said closure member to one of said openand closed positions, to a position closing both of said upper and lowerapertures; and at least one of the closing means including holding meansresponsive to line pressure for maintaining said closing means in saidposition closing said lower aperture, said holding means including alost motion connection between the corresponding stem and the closuremember.
 31. In a valve comprising a body having inlet and outletconduits and upper and lower stem apertures with a chamber therebetween,a closure member disposed in said chamber and movable between an openposition wherein fluid flow is permitted through said chamber and intosaid outlet conduit and a closed position wherein such flow isprevented, upper and lower stems on said closure member extendingthrough said upper and lower apertures, respectively, an upper bonnetcovering the upper aperture, a lower cap covering the lower aperture,and means connected to one of said stems adapted to move said stemslongitudinally and thereby move said closure member between open andclosed positions, the improvement which comprises:closing means on saidstems movable, upon movement of said closure member to one of said openand closed positions, to a position closing both of said upper and lowerapertures; and a lost motion connection between the upper and lowerstems allowing limited axial relative movement, whereby both of theupper and lower apertures can be held closed at the same time.
 32. Avalve, comprising:a valve body having an inlet and an outlet and upperand lower apertures with a chamber therebetween; closure means forpreventing flow through said chamber into said outlet in the closedposition and permitting flow through said chamber into said outlet inthe open position; a seat disposed within the chamber and housing aportion of said closure means; moving means for moving said closuremeans between the open and closed positions; first and second capmembers closing said upper and lower apertures; said closure meansextending through said chamber and said upper and lower apertures andinto said first and second cap members; double seal ring means on saidclosure means providing a metal-to-metal sealing engagement with saidfirst cap member in both the open and closed positions; single seal ringmeans on said closure means providing a metal-to-metal sealingengagement with said valve body at said lower aperture in one of theopen and closed positions; and said double seal ring means is actuatedby said moving means and said single seal ring means is actuated by linepressure.
 33. A valve, comprising:a valve body having an inlet and anoutlet and upper and lower apertures with a chamber therebetween;closure means for preventing flow through said chamber into said outletin the closed position and permitting flow through said chamber intosaid outlet in the open position; a seat disposed within the chamber andhousing a portion of said closure means; moving means for moving saidclosure means between the open and closed positions; first and secondcap members for closing said upper and lower apertures; said closuremeans extending through said chamber and said upper and lower aperturesand into said first and second cap members; double seal ring means onsaid closure means providing a metal-to-metal sealing engagement withsaid first cap member in both the open and closed positions; single sealring means on said closure means providing a metal-to-metal sealingengagement with said valve body at said lower aperture in one of theopen and closed positions; said double seal ring means being positionedto initiate sealing engagement with said first cap member after thesealing engagement by said single seal ring with said valve body.
 34. Avalve, comprising:a valve body having an inlet and an outlet and upperand lower apertures with a chamber therebetween; closure means forpreventing flow through said chamber into said outlet in the closedposition and permitting flow through said chamber into said outlet inthe open position; a seat disposed within the chamber and housing aportion of said closure means; moving means for moving said closuremeans between the open and closed positions; first and second capmembers closing said upper and lower apertures; said closure meansextending through said chamber and said upper and lower apertures andinto said first and second cap members; double seal ring means on saidclosure means actuable by said moving means to provide a metal-to-metalsealing engagement with said first cap member in both the open andclosed positions; and line-pressure actuable single seal ring means onsaid closure means providing a metal-to-metal sealing engagement withsaid valve body at said lower aperture in one of the open and closedpositions.